Prolactin and the dietary protein/carbohydrate ratio regulate the expression of SNAT2 amino acid transporter in the mammary gland during lactation

Abstract

The sodium coupled neutral amino acid transporter 2 (SNAT2/SAT2/ATA2) is expressed in the mammary gland (MG) and plays an important role in the uptake of alanine and glutamine which are the most abundant amino acids transported into this tissue during lactation. Thus, the aim of this study was to assess the amount and localization of SNAT2 before delivery and during lactation in rat MG, and to evaluate whether prolactin and the dietary protein/carbohydrate ratio might influence SNAT2 expression in the MG, liver and adipose tissue during lactation. Our results showed that SNAT2 protein abundance in the MG increased during lactation and this increase was maintained along this period, while 24 h after weaning it tended to decrease. To study the effect of prolactin on SNAT2 expression, we incubated MG explants or T47D cells transfected with the SNAT2 promoter with prolactin, and we observed in both studies an increase in the SNAT2 expression or promoter activity. Consumption of a high-protein/low carbohydrate diet increased prolactin concentration, with a concomitant increase in SNAT2 expression not only in the MG during lactation, but also in the liver and adipose tissue. There was a correlation between SNAT2 expression and serum prolactin levels depending on the amount of dietary protein/carbohydrate ratio consumed. These findings suggest that prolactin actively supports lactation providing amino acids to the gland through SNAT2 for the synthesis of milk proteins.

Free Amino Acids in Human Milk: A Potential Role for Glutamine and Glutamate in the Protection Against Neonatal Allergies and Infections

“…Whereas, FAA levels seem to be independent of the mothers' age (64), maternal body-mass index is reported to slightly influence levels of several FAAs (65,66). Mechanisms underlying this effect are not known, but may involve the hormone prolactin, as prolactin is involved in regulating FAA transport in the mammary gland and levels of prolactin associate with maternal body-mass index (67)(68)(69). Studies investigating the effect of maternal diet on the AA composition in human milk indicate that the TAA composition is largely independent of the AA composition of the diet (70,71).…”

Prolactin regulates LAT1 expression via STAT5 (signal transducer and activator of transcription 5) signaling in mammary epithelial cells of dairy cows

“…In rat mammary gland, PRL has an important role in the regulation of AA uptake (Viña et al, 1981). The sodiumcoupled neutral amino acid transporter 2 (SNAT2) is characterized as a classical system A transporter and is important for the uptake of small neutral AA into the mammary gland to promote cell proliferation during gestation and to induce milk protein synthesis during lactation (Velázquez-Villegas et al, 2014). Studies in mammary gland explants from lactating rats have demonstrated that PRL treatment increases SNAT2 mRNA and protein abundance (Velázquez-Villegas et al, 2015).…”

“…The sodiumcoupled neutral amino acid transporter 2 (SNAT2) is characterized as a classical system A transporter and is important for the uptake of small neutral AA into the mammary gland to promote cell proliferation during gestation and to induce milk protein synthesis during lactation (Velázquez-Villegas et al, 2014). Studies in mammary gland explants from lactating rats have demonstrated that PRL treatment increases SNAT2 mRNA and protein abundance (Velázquez-Villegas et al, 2015). In the current study, we found that mRNA levels of LAT1 in cultured mammary epithelial cells of dairy cows were increased with increasing concentrations of PRL and peaked at 5 μg/mL PRL.…”

Restraint stress in lactating mice alters the levels of sulfur-containing amino acids in milk

“…Taurine is contained in large amounts in milk, especially in the colostrum [ 25 ]. It has been reported that the mRNA of amino acid transporters is expressed in the mammary gland [ 2 , 28 ] and that their transporters transfer free amino acids from maternal blood to milk. The large amount of taurine in the milk seems to derive from 1) maternal blood via taurine transporters, and 2) the mammary glands.…”